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106 lines
2.0 KiB
Elm
106 lines
2.0 KiB
Elm
module Util.List exposing
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( distinct
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, dropRight
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, find
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, findIndexed
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, findNext
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, findPrev
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, get
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, sliding
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)
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get : List a -> Int -> Maybe a
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get list index =
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if index < 0 then
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Nothing
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else
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case list of
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[] ->
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Nothing
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x :: xs ->
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if index == 0 then
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Just x
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else
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get xs (index - 1)
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find : (a -> Bool) -> List a -> Maybe a
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find pred list =
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findIndexed pred list |> Maybe.map Tuple.first
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findIndexed : (a -> Bool) -> List a -> Maybe ( a, Int )
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findIndexed pred list =
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findIndexed1 pred list 0
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findIndexed1 : (a -> Bool) -> List a -> Int -> Maybe ( a, Int )
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findIndexed1 pred list index =
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case list of
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[] ->
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Nothing
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x :: xs ->
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if pred x then
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Just ( x, index )
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else
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findIndexed1 pred xs (index + 1)
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distinct : List a -> List a
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distinct list =
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List.reverse <|
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List.foldl
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(\a ->
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\r ->
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if List.member a r then
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r
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else
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a :: r
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)
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[]
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list
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findPrev : (a -> Bool) -> List a -> Maybe a
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findPrev pred list =
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findIndexed pred list
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|> Maybe.map Tuple.second
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|> Maybe.map (\i -> i - 1)
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|> Maybe.andThen (get list)
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findNext : (a -> Bool) -> List a -> Maybe a
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findNext pred list =
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findIndexed pred list
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|> Maybe.map Tuple.second
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|> Maybe.map (\i -> i + 1)
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|> Maybe.andThen (get list)
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dropRight : Int -> List a -> List a
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dropRight n list =
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List.reverse list
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|> List.drop n
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|> List.reverse
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sliding : (a -> a -> b) -> List a -> List b
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sliding f list =
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let
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windows =
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case list of
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_ :: xs ->
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List.map2 Tuple.pair list xs
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_ ->
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[]
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in
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List.map (\( e1, e2 ) -> f e1 e2) windows
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